U.S. Pat. No. 4,507,453 to Tom and U.S. Pat. No. 4,400,340 to Klosiewicz disclose a new species of thermoset polymers based on dicyclopentadiene monomer which polymers are noteworthy for their unusually good balance of high impact strength and high modulus. These polymers are prepared at low temperatures and under low pressures using a metathesis catalyst system comprising a tungsten or molybdenum catalyst activated by an alkyl aluminum compound. Thanks to the aforementioned unusual balance of modulus and impact strength these polymers based on dicyclopentadiene are commercially desirable materials and they are becoming increasingly sought after for use in molding of shaped articles in complex configurations.
Molding of shaped articles of dicyclopentadiene is carried out by injecting liquid streams of the monomer formulated with catalyst and activator components into an appropriately shaped mold wherein the monomer polymerizes to form the desired shape directly. This can be done via a two-stream process as taught in the cited Tom patent or, with appropriate moderation of the reaction rate, via a one-stream process.
A problem that has been encountered in carrying out the polymerizations as discussed arises out of the fact that dicyclopentadiene melts at 32.degree. C. and is thus a solid at room temperature. Accordingly, it must be heated prior to formulation with catalysts, activators and other additives and must be transported through heat-jacketed lines to maintain a liquid state. A significant process improvement can be effected both in terms of handling ease and plant investment if the monomer can be handled as a liquid at room temperatures and below.
It is known that contaminants or adulterants of many kinds, when incorporated into a solid organic material, depress the melting point by a specific calculable amount. However, most adulterants that might be added to dicyclopentadiene in sufficient amounts to accomplish this reduction interfere with, or even prevent, metathesis polymerization from taking place. Those that doesn't prevent polymerization generally have an undesirable effect on the properties of the polymer.
It is the object of this invention to prepare dicyclopentadiene which is liquid at temperatures below 20.degree. C. wherein the adulterant is an oligomer or a mixture of oligomers of cyclopentadiene which are copolymerizable with dicyclopentadiene. It is a further object to provide a method of preparing the aforesaid adulterated dicyclopentadiene. Yet, another object is to prepare a metathesis polymerizable liquid mixture containing a predominant amount of dicyclopentadiene.
In the description which follows, the term "oligomers" or "cyclopentadiene oligomers" is intended to mean cyclopentadiene oligomers higher than dicyclopentadiene.